View Full Version : Modifying the float in a gt carb
Old skool mod really, but been rebuilding me carb. Done the old second stage jobbie to 1.2mm but the old mod was to tweak the float. Where the pin runs thro there is a small upstand and you can shave a bit off to allow more fuel into the chamber. Is it worth it and will it make enough difference ?? Might need an old skool member to answer this 😜
Cheers
B18ftMOJO5
05-07-2015, 18:25
Haz would most likely know. Try to pm him.:agree:
bigdavec1974
05-07-2015, 19:43
If your worried about emptying the carb just add a malpassi fpr and up the fuel pressure from 4 to 6.
Worked for me :)
Or a 2mm needle valve but not both will cause issues for sure
Well done the mod anyhow . Second stage drilled 1.2 0.9 a/c 120main float mod at wot 11.9:agree:afr 20psi . Got a malpassi fpr Nd bosch 044 cossi pump 😀
Float sits a tad higher allowing more fuel into the chamber. Have only taken 3mm off. Anymore then the chamber may over fill
V cool :) Good pics too. :agree:
V cool :) Good pics too. :agree:
Cheers trev , my photography isn't zee best lol just thought some pics may help others doing the same thing 😀👍
Picture of the second stage once drilled
Had a couple of pm'a asking which bit was ground down by 3mm. In the picture you can see there is a small raised piece of plastic on top of the float near the pin. That's the part I ground down to gain a little more fuel.as that's where the ball bearing hits as such. It was an old mod years ago. Up to you if you want to try it. Iv done it and the float defently sits up higher.
francob80
06-07-2015, 11:17
Well done the mod anyhow . Second stage drilled 1.2 0.9 a/c 120main float mod at wot 11.9:agree:afr 20psi . Got a malpassi fpr Nd bosch 044 cossi pump 😀
Didn't Phil's go bang at 12.0 AFR?
The more the afr leans off means you can run a tad more boost as running richer helps cool the engine for track use. It's just finding the correct point for your use and what it's being used for . Optimum / safe zone as such. I belive for everyday use you need to aim for 13's on the afr . Mine at the mo is on 20psi at wot 4th its 11.9 but havnt tried 5th which is what is recomended but I havnt many roads near me to do that. But my idle is between 14.5 -14.8 on afr . So I belive for a home jobbie without being setup on the dyno that's pretty good .
Any criticism / advice greatly taken 😀
Didn't Phil's go bang at 12.0 AFR?
I think he was run around 24, 25 psi. A bit of a difference there. :eek:
The best tuned extra van in the world !!! 😜👍 any comments from you brigsy is greatly taken!!:worship::worship:
michael tierney
06-07-2015, 14:15
the detonation will kill the engine also:(
Pink marking around the holes in the 2nd stage drilling
Did you enlarge them to the lines?
Pink marking around the holes in the 2nd stage drilling
Did you enlarge them to the lines?
My poor cleaning I'm afraid , the gasket was stained to the alloy, normal tho.I cleaned it right up once drilled the second stage,as sometimes swaf can get in the carb. You can play with the 3rd stage on the carb but iv never had good results from enlarging it. If you are doin standing quarters then it's worth playing with 😀
Old skool mod really, but been rebuilding me carb. Done the old second stage jobbie to 1.2mm but the old mod was to tweak the float. Where the pin runs thro there is a small upstand and you can shave a bit off to allow more fuel into the chamber. Is it worth it and will it make enough difference ?? Might need an old skool member to answer this ��
Cheers
I dare say this mod won't allow for more fuel - only the level. The problem you can have with running a lot of boost (18+ psi) is the carb bowl emptying. The way round this is to either run a Malpassi FPR and/or replace the needle jet with a larger one.
Are you going to check for det as well? :)
Your ac jet is huge as in standing out of emulsion tube. Where did you buy it from?
I'm currently making AC jets of various sizes and mine dont stick out that far
Your ac jet is huge as in standing out of emulsion tube. Where did you buy it from?
I'm currently making AC jets of various sizes and mine dont stick out that far
Came from mike at Gtturbospares. I thought it stuck up to much myself but iv been told it's not an issue
Interesting cheers
I've been making my stock of jets the same as factory but if I can get away with a little more height out the emulsion tube it'll make slotting for the screwdriver much easier
I can't imagine that causing an issue as the hole is still the same size. It would be easier to remove, I agree :agree:
I have run an AC bet that doesn't sit flush in the carb, makes no difference that I could spot. Yes mine did go pop at flat 12 afr (cracked liner) that was at 6.8/7k in fourth with 24/25psi.
It actually happened on the run off at pod, that was full throttle launch and full throttle changes all the way up the strip. I still need to double check everything to make sure it was actually lack of fuel that caused it. There was no sign of det at all the gasket was fine the lot. Was a bit puzzled if I'm honest.
I'm on it tho with exactly what I need to check and change of needs be to try and stop it doing it again.
When the bowl empty's it will do it at 20lb or so boost with o.e comp and a 285 cam at the top of fourth so if you at 11.9 at solid upto 7k rpm then you have probably cured the bowl emptying issue :agree:
Be careful in Fifth, it will happen a little sooner than in fourth. You might get away with it at 20lb boost once the boost gets past 22psi even the upped fuel pressure won't stop the bowl from emptying in Fifth. I top ended mine for about 2mins full throttle on my last engine at 24lb. Melted no 4 piston. :disagree: Carbs and top end runs don't mix with high boost.
I have run an AC bet that doesn't sit flush in the carb, makes no difference that I could spot. Yes mine did go pop at flat 12 afr (cracked liner) that was at 6.8/7k in fourth with 24/25psi.
It actually happened on the run off at pod, that was full throttle launch and full throttle changes all the way up the strip. I still need to double check everything to make sure it was actually lack of fuel that caused it. There was no sign of det at all the gasket was fine the lot. Was a bit puzzled if I'm honest.
I'm on it tho with exactly what I need to check and change of needs be to try and stop it doing it again.
When the bowl empty's it will do it at 20lb or so boost with o.e comp and a 285 cam at the top of fourth so if you at 11.9 at solid upto 7k rpm then you have probably cured the bowl emptying issue :agree:
Be careful in Fifth, it will happen a little sooner than in fourth. You might get away with it at 20lb boost once the boost gets past 22psi even the upped fuel pressure won't stop the bowl from emptying in Fifth. I top ended mine for about 2mins full throttle on my last engine at 24lb. Melted no 4 piston. :disagree: Carbs and top end runs don't mix with high boost.
How new were the pistons and liners. If they were new did you run them in a lot. May have been a bit tight. Sometimes its best to run a bit more clearance in the bore when running higher boost/power.
The best tuned extra van in the world !!! 😜👍 any comments from you brigsy is greatly taken!!:worship::worship:
As much as I would like to, I cannot take credit for Brigsy van :wasntme: He is a star :cool:
How new were the pistons and liners. If they were new did you run them in a lot. May have been a bit tight. Sometimes its best to run a bit more clearance in the bore when running higher boost/power.
The bottom end was from what I could gather original, the honing marks in the liners were non existent so it had definitely done some miles. Makes the best oil pressure i have ever seen from a C1j before tho. 49/50psi at 3k rpm. So it was definitely healthy, even with the liners having done some miles it hardly breathes either almost zero oil in the catch tank after 500 miles of abuse.:agree:
B18ftMOJO5
08-07-2015, 15:14
As much as I would like to, I cannot take credit for Brigsy van :wasntme: He is a star :cool:
Yup that van sounded awesome at scoff rr day:agree:
francob80
09-07-2015, 10:52
I have run an AC bet that doesn't sit flush in the carb, makes no difference that I could spot. Yes mine did go pop at flat 12 afr (cracked liner) that was at 6.8/7k in fourth with 24/25psi.
It actually happened on the run off at pod, that was full throttle launch and full throttle changes all the way up the strip. I still need to double check everything to make sure it was actually lack of fuel that caused it. There was no sign of det at all the gasket was fine the lot. Was a bit puzzled if I'm honest.
I'm on it tho with exactly what I need to check and change of needs be to try and stop it doing it again.
When the bowl empty's it will do it at 20lb or so boost with o.e comp and a 285 cam at the top of fourth so if you at 11.9 at solid upto 7k rpm then you have probably cured the bowl emptying issue :agree:
Be careful in Fifth, it will happen a little sooner than in fourth. You might get away with it at 20lb boost once the boost gets past 22psi even the upped fuel pressure won't stop the bowl from emptying in Fifth. I top ended mine for about 2mins full throttle on my last engine at 24lb. Melted no 4 piston. :disagree: Carbs and top end runs don't mix with high boost.
Good info as always Phil.
The bottom end was from what I could gather original, the honing marks in the liners were non existent so it had definitely done some miles. Makes the best oil pressure i have ever seen from a C1j before tho. 49/50psi at 3k rpm. So it was definitely healthy, even with the liners having done some miles it hardly breathes either almost zero oil in the catch tank after 500 miles of abuse.:agree:
Maybe it's just the fact that the liners were old and not as strong as they once were? I remember when I cracked a liner in 2006, I'd just come back from a R/R day and all went well - good fuelling etc and it popped on the way back. I saw no pitting/det marks or gasket damage, just a big crack in pot 3 liner. It had 118k on the clock at that point.
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